The present invention pertains generally to beam choppers, and pertains more particularly to systems for chopping a beam of radiant energy into three or more beams of approximately the same strength and cross-sectional size and shape.
Systems for chopping a beam of radiant energy into two or more series of energy pulses are well known. To produce n beams by chopping conventionally requires n annuli of alternating transmissive and reflective segments. The annuli may be disposed on one or on several discs. One system, which uses for this purpose a multiplicity of beam chopping discs each having a single such chopper ring is disclosed in U.S. Pat. No. 4,118,619, issued Oct. 3, 1978. A second embodiment disclosed in U.S. Pat. No. 4,118,619 includes a single disc with a plurality of concentric rings of alternating transmissive and reflective portions. United Kingdom Patent Application No. 2,032,323A, published May 8, 1980, and assigned in common with the present application, discloses another type of beam chopping system, using a disc having a beveled edge which defines the chopper ring, the disc axis being inclined at an angle to the incident beam. A similar system in which the disc axis is parallel to the beam is disclosed in published European Patent Application No. EPO 0021165 (PM813D), published Jan. 7, 1982, and assigned in common herewith.
In the known systems mentioned above, it is necessary either to have as many discs as the number of beams desired or to provide at least one disc with several concentric rings of alternating reflective and transmissive portions, as is disclosed in U.S. Pat. No. 4,118,619. As can be seen from that patent, the latter arrangement requires a respective auxiliary mirror to reflect each reflected beam back to the disc for further chopping, introducing serious problems of alignment. It would be desirable to provide a beam chopping system capable of chopping an incident beam into any desired number of chains of energy pulses traveling along different paths, using only a single disc, and avoiding the need for ultra-sensitive alignment of auxiliary optics to which the one-disc, multi-chopper-ring arrangement disclosed in U.S Pat. No. 4,118,619 is subject.